Telecommunication system and a method for matching the numbering schemes of two telecommunication systems

ABSTRACT

The invention relates to a telecommunication system and a method for matching the numbering schemes of telecommunication systems. The telecommunication system comprises a transmission network comprising at least one mobile exchange (MSC1, MSC2) associated with a subsystem (BUC, BU1-BU6), the calls of subscribers (MT1-MT6) in the subsystem being routed through the transmission network and the mobile exchange. A numbering scheme of the subsystem comprises an X-bit binary subscriber identity code (PID) and a numbering scheme of the transmission network comprises a Y-decimal subscriber identity code (MSIN). In the transmission network the subscriber (MT1-MT6) of the subsystem is assigned a Y-decimal identity code comprising a decimal number derived from the X-bit binary identity code of the subscriber and having no more than Y-1 decimals. At least one system identification decimal is introduced into the obtained decimal number at a predetermined position to indicate that the identity code belongs to the subscriber (MT1-MT6) of the subsystem.

FIELD OF THE INVENTION

The invention relates to a method for matching the numbering scheme of atelecommunication system with the numbering scheme of anothertelecommunication system at an interface between the systems.

BACKGROUND OF THE INVENTION

Cordless telephone (CT) systems such as the digital cordless telephonesystem CT2 have recently come out on the market. The CT system comprisesa base station connected to a subscriber line in a public switchedtelephone network (PSTN). There are three different types of basestations: a residential (home) base station, a base station connected toa private branch exchange (PBX) in an office or operating independentlyas a PBX, and so-called telepoint base stations, by means of whichoutward calls only are possible for a CT telephone.

As the present-day CT systems are regarded as PSTN subscriberconnections (access points), a call is addressed to the CT terminalequipment in a normal way by dialing a telephone number in accordancewith the PSTN numbering scheme. On the basis of the telephone number thePSTN thereby routes the call to a respective subscriber connection towhich the CT residential base station or the PBX of the CT office basestation is connected. The base station pages the CT terminal equipmentover the radio path by means of a identity code determined by thenumbering scheme of the CT system, and sets up a call when the terminalequipment responds. In practice, it is thus possible to make a call tothe CT terminal equipment only through its residential or office basestations (through predetermined subscriber connections).

When the CT terminal equipment desires to set up a call, it establishesa connection to the base station, which checks the authenticity and userrights of the terminal equipment by means of an equipment specificidentity code assigned in accordance with the CT numbering scheme,before it connects the terminal equipment "on line" to the PSTNsubscriber connection. Thereafter the terminal equipment can dial thetelephone number to which the call is addressed in a conventional mannerin accordance with the PSTN numbering scheme.

Accordingly, the numbering schemes of the present CT systems serve onlythe CT radio link and are not utilized anywhere in the PSTN.

In the future it may become advantageous to be able to connect CTsystems even to mobile radio networks. As there are no addressableaccess points (such as PSTN subscriber connections) but only trafficchannels used commonly by all mobile subscriber equipments in the mobileradio network, the setup of a call is always based on the use of anidentity code assigned to the subscriber equipment.

A problem therewith is, however, that the numbering schemes specifiedfor the cordless telephone system and for the mobile radio system areusually quite different and incompatible. Integrating such systems wouldrequire matching of the numbering schemes.

SUMMARY OF THE INVENTION

An object of the invention is to match such different numbering schemesas efficiently and as simply as possible.

A further object of the invention is to utilize the inherent identityinformation of the terminal equipment of the cordless telephone systemin such a way that compatibility with the procedure used in theidentification of the mobile terminal equipment in the mobile radionetwork is obtained.

This is achieved by means of a method according to the invention,wherein in the second telecommunication system the subscriber/equipmentof the first telecommunication system is assigned a Y-decimal identitycode obtained by converting the X-bit binary identity code of thesubscriber/equipment into a decimal number comprising no more than Y-1decimals, and by introducing one or more system identification decimalsto the obtained decimal number at a predetermined position, the systemidentification decimal(s) indicating that the subscriber/equipmentidentity code belongs to the subscriber/equipment of the firsttelecommunication system.

The invention also relates to a telecommunication system comprising atransmission network utilizing a first numbering scheme and comprisingat lest one mobile exchange connected to a subsystem utilizing adifferent numbering scheme, the calls of subscribers in the subsystembeing routed through the transmission network and said mobile exchange.According to the invention, the system is characterized in that thenumbering scheme of the subsystem comprises an X-bit binarysubscriber/equipment identity code, and the numbering scheme of thetransmission network comprises a Y-decimal subscriber/equipment identitycode; and that in the transmission network the subsystemsubscriber/equipment is assigned a Y-decimal identity code comprising adecimal number derived from the X-bit binary identity code of thesubscriber/equipment and including no more than Y-1 numbers, at leastone system identification decimal code being added to the obtaineddecimal number at a predetermined position, the system identificationcode(s) indicating that the identity code belongs to thesubscriber/equipment of the subsystem.

By means of the invention, a unique subscriber identity code for thefixed transmission network can be derived from the binary subscriberidentity code of the subsystem by a simple algorithm. Correspondingly,the unique subsystem subscriber identity code can be restored from thesubscriber identity code of the fixed transmission network by an inversealgorithm. The algorithms are valid for all subsystem subscriberidentities, and the fixed transmission network identities derived fromthem, and so it is possible to avoid e.g. the need to use largeconversion tables difficult to update. Conversions can be performedidentically at all intersystem interfaces; the only requirement is thatthe conversion algorithms are similar everywhere.

The subscriber identity codes of the subsystem can be assigned in anormal way completely independently of the numbering of the fixedtransmission network. The numbering schemes of both systems can bemaintained unchanged so that they comply with the respectivespecifications. As the decimal numbers derived from the subscriberidentity codes of the subsystem are provided with a special subsystemidentification number, it is ensured that the obtained fixedtransmission network identity is unique and that the fixed transmissionnetwork is able to identify certain subscriber identities as subsystemsubscriber identities, e.g. for special network functions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described by means ofillustrating embodiments with reference to the attached drawings, inwhich

FIG. 1 illustrates schematically a cellular mobile radio network inwhich the method according to the invention may be applied;

FIG. 2 is a block and flow diagram illustrating the method according tothe invention for matching the numbering schemes in the system shown inFIG. 1; and

FIGS. 3 and 4 are block diagrams illustrating IMSI/PID and PID/IMSIconverters which can be used in the system shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In the text below the invention will be described by means of an examplein which a digital cordless telephone system CT2 is connected to formpart of the digital cellular mobile radio system GSM, which is theprimary application of the invention. The method according to theinvention can, however, also be applied when connecting other cordlesstelephone systems, such as the DECT (Digital European CordlessTelephone) to the GSM or its modifications or to other similar mobileradio systems or switched transmission networks (e.g. ISDN).

The basic structure and basic functions of the GSM mobile radio systemare well-known to one skilled in the art and relatively accuratelydefined in the specifications of the GSM system. In the following a fewbasic concepts and elements of the GSM system will be defined withreference to FIG. 1. An area within which the GSM mobile radio servicesare available is called a GSM network (GSM service area), which maycover several countries. The GSM network may be divided into nationalGSM networks (PLMN service area), i.e. areas covered by one operatoroffering GSM services. There may also be several GSM networks in thesame country and the areas covered by them may overlap geographically.In the text below, the GSM network primarily refers to such a "national"network.

The GSM network may comprise one or more MSC areas, i.e. areas withinwhich services are provided by a single mobile services switching centreMSC (mobile exchange). The MSC area, in turn, may be divided into one ormore location areas each covered by one or more radio cells. The cell isthe smallest geographical area of the system, comprising one or morefixed radio stations, i.e. base stations, and using predetermined radiochannels.

The GSM network comprises at least one home location register (HLR),which is a data base in which subscriber data, such as location data,are stored permanently. The system also comprises several visitorlocation registers (VLR) each associated with one or more central areas.However, each MSC area has a single VLR. The VLR is a data base in whichsubscriber data are stored while the mobile station MS visits the areaof the VLR. The VLR stores information of the location of the mobilestation MS with the accuracy of one location area. The HLR, in turn,stores information of the VLR that the mobile radio visits and itprovides routing data for routing mobile stations MS terminating callsin the network. The HLR, in turn, receives the required routing datafrom the VLR. The HLR and the VLR have only a signalling connection tothe other components of the mobile radio network.

Within the GSM network the subscriber identification is based on theInternational Mobile Subscriber Identity IMSI, which comprises a GSMMobile Country Code MCC (three digits), a Mobile Network Code MNC (2digits) of the national GSM network, and a Mobile Station IdentificationNumber MSIN (ten digits). The MSIN is unique within a certain nationalGSM network and can be specified by the network operator.

FIG. 1 illustrates two MSC areas, one with a MSC1 and a VLR1 and theother with a MSC2 and a VLR2 for the traffic control. There are one ormore location areas under the MSC area covered by both the MSC1 andMSC2, and each location area comprises a base station controller BSC1and BSC2, respectively, which controls several fixed radio stations,i.e. base transceiver stations BTS. Each radio cell comprises one BTS,and one base station controller BTC provides services for several cells.A mobile station MS located in the cell establishes a two-way radio linkto the BTS of the cell. Both a signalling connection and speech channelsare provided between the BSC and the MSC.

The GSM network is usually connected to other networks, such as thepublic telephone network (PSTN), another mobile network (PSPDN) or anISDN network through a certain MSC called a gateway MSC.

According to the invention the cordless telephone system CT2 isintegrated as a subsystem for the GSM system by connecting the CT2 basestations BU under the control of the MSC. In FIG. 1, the CT2 basestations BU1, BU2 and BU3 are connected to the MSC1, and the CT2 basestations BU4 and BU5 are connected to the MSC2. The CT2 base stationcontroller BUC is also connected to the MSC2. In practice, the BUC maybe e.g. a telephone exchange PABX operating in compliance with the CT2specification and controlling base stations BU5-BU6. The mobile servicesswitching centres MSC and the CT2 base stations BU and base stationcontrollers BUC are provided with suitable additional equipment andsoftware for combining the mobility functions of the systems and formatching the number schemes of the systems.

In principle, the GSM transmission network may handle CT2 subscriberssimilarly as actual GSM subscribers although the CT2 and GSM systems arefully separate radio systems at least on the radio path level.

The CT2 system and the GSM system, however, have completely differentnumbering schemes, and so the CT2 subscriber identity codes cannot beused as such in the GSM network.

In the CT2 system the CT2 terminal equipment identity code is a binary27-bit PID (Portable Identity Code) which, in turn, comprises twoportions: an 8-bit MIC (Manufacturer Identity Code) and a 19-bit HIC(Handset Identity Code). This code is used in compliance with the CT2Common Air Interface (CAI) specification over the radio path between theCT2 base station BU and the CT2 terminal equipment MT. The CAIspecification is described e.g. in CT2 Common Air Interface, M. W.Evans, British Telecommunications Engineering, Vol. 9, July 1990, p.103-111.

According to the invention, each CT2 terminal equipment is assignedanother subscriber identity code for the GSM system, which identity codecorresponds to the GSM IMSI. This identity code has to be unique in theGSM network, and it has to be convertible into a CT identity code andagain restored at all interfaces between these systems.

In the following the conversion of the PID into the IMSI (PID/IMSIconversion) according to the invention will be described with referenceto FIG. 2:

i) A 27-bit binary PID is converted into decimal number (maximum value134217727), which requires no more than 9 decimals. In the decimalnumber (usually a BCD number) so obtained, the non-significant zeros aremaintained in front of the significant numbers, and so the decimalnumbers are always presented with 9 decimals, and the IMSI associatedwith the CT2 terminal equipment is unambiguous within the entire area ofthe GSM network (i.e. globally unambiguous).

ii) A CT2 System identity number N, by means of which the GSM system isable to distinguish a CT2 subscriber from GSM subscribers, is added at adesired position to the 9-decimal number produced as described underitem i), e.g. as the most significant number. This results in a10-number decimal number which forms an MSIN complying with the GSMspecifications.

iii) First the network code MNC and then the country code MCC are addedto the MSIN produced as described under item ii) as the most significantnumbers, thus obtaining an IMSI complying with the GSM specifications,which can be used as such as a CT2 terminal equipment identity code inthe GSM network.

The IMSI is converted into the PID (IMSI/PID conversion) by performingthe inverse conversions of the conversions i-iii in reverse order.

The final IMSI is always formed at the latest in the MSC, so that theIMSI is used for the CT2 terminal equipment everywhere in the GSMnetwork outside the MSCs. On the other hand, the PID is always used overthe radio path between the BU and the MT. The functions required for thePID/IMSI and IMSI/PID conversions can, in principle, be shared in anyway between the BU or BUC and the MSC.

In the preferred embodiment of the invention shown in FIG. 2, wherethere is provided an ISDN interface between the BU and the MSC, theconversion i) is performed at the CT2 base station BU so that a decimalnumber can be transferred through the ISDN interface. The mobileservices switching centre MSC performs items ii) and iii) by adding theCT2 system identity number N and the GSM network and country codes MCCand MNC to the decimal number.

Alternatively, the BU may perform the conversion steps i) and ii) or allthe conversion steps i) through iii).

Another alternative is to utilize the binary PID in the datatransmission between the BU and the MSC and perform all conversion stepsi) through iii) in the MSC.

In the preferred embodiment of the invention, the conversions areperformed by software, although they may also be performed by thecircuit arrangements shown in FIGS. 3 and 4, for instance.

In FIG. 3, a binary/decimal converter 31 performs the conversion i) andthe conversion result is applied to the input of a latch circuit 32 asthe 9 least significant decimals. The number N, which is a preselectedconstant, is applied to the input of the latch circuit 32 as thefollowing more significant decimal, so that a 10-decimal MSIN isobtained in the output of the latch circuit 32 (conversion ii).Correspondingly, the MCC and the MNC are fed in the input of a latchcircuit 33 in front of the MSIN as the more significant decimals, sothat the output will give the IMSI (conversion iii). In FIG. 4, the IMSIis fed to the input of a latch circuit 42, whereas only the 9 leastsignificant decimals are fed from the output of the latch circuit 42(inverse conversions iii and ii) to a decimal/binary converter 41, sothat the output of the converter 41 will give the binary PID (inverseconversion i).

Generally speaking, the invention is suitable for the conversion of anyX-bit binary subscriber identity code into a decimal number comprisingno more than Y-1 decimals, to which at least one subsystem identitynumber N is added so that a Y-decimal subscriber identity code of theother system is obtained, the possible network and country codes beingadded to the subscriber identity code. X and Y are thereby determined onthe basis of the numbering schemes to be matched in each particularcase. In the example above, Y=10 and X=27.

The subscriber identity code may herein refer to either a subscriberspecific identity code or to a terminal specific identity code,depending on the systems to be integrated in each particular case.

The drawings and the description related to them are only intended toillustrate the present invention. In their details, the method and thetelecommunication system according to the invention may vary within thescope of the attached claims.

I claim:
 1. A method for matching the numbering scheme of atelecommunication system with the numbering scheme of anothertelecommunication system at an interface between the systems, thenumbering scheme of the first telecommunication system comprising anX-bit binary subscriber/equipment specific identity code, and thenumbering scheme of the second telecommunication system comprising aY-decimal subscriber/equipment specific identity code, characterized inthat in the second telecommunication system the subscriber/equipment ofthe first telecommunication system is assigned a Y-decimal identity codeobtained by converting the X-bit binary identity code of thesubscriber/equipment into a decimal number comprising no more than Y-1decimals, and by introducing one or more system identification decimalsinto the obtained decimal number at a predetermined position, the systemidentification decimal(s) indicating that the subscriber/equipmentidentity code belongs to the subscriber/equipment of the firsttelecommunication system.
 2. A method according to claim 1,characterized in that a network code and/or country code is utilized inthe subscriber/equipment identity code used in the second system.
 3. Amethod according to claim 1 or 2, characterized in that Y=10, X=27, andthat the 27-bit binary identity code is converted into a 9-numberdecimal number and one system identification decimal is introduced asthe most significant decimal to obtain a 10-decimal number.
 4. Atelecommunication system comprising a transmission network utilizing afirst numbering scheme and comprising at least one mobile exchange(MSC1, MSC2) connected to a subsystem (BUC, BU1-BU6) utilizing adifferent numbering scheme, the calls of subscribers (MT1-MT6) in thesubsystem being routed through the transmission network and said mobileexchange, characterized in that the numbering scheme of the subsystemcomprises an X-bit binary subscriber/equipment identity code (PID), andthe numbering scheme of the transmission network comprises a Y-decimalsubscriber/equipment identity code (MSIN); and that in the transmissionnetwork the subsystem subscriber/equipment is assigned a Y-decimalidentity code comprising a decimal number derived from the X-bit binaryidentity code of the subscriber/equipment and including no more than Y-1numbers, at least one system identification decimal code being added tothe obtained decimal number at a predetermined position, the systemidentification code(s) indicating that the identity code belongs to thesubscriber/equipment (MT1-MT6) of the subsystem.
 5. A system accordingto claim 4, characterized in that a network code and/or country code(MNC, MCC) is utilized as the most significant decimals in thesubscriber/equipment identity code (IMSI) in the numbering scheme of thetransmission system.
 6. A system according to claim 4, characterized inthat the subsystem is a cordless telephone system comprising at leastone fixed radio station (BU1-BUS) and at least one subscriber radiostation (MT1-MT6), and that said binary subscriber/equipment identitycode (PID) is used in the communication between the fixed radio station(BU1-BUS) and the subscriber radio station (MT1-MT6).
 7. A systemaccording to claim 6, characterized in that the decimal number versionof the binary subscriber/equipment identity code (PID) is used in thecommunication between the subsystem and the associated mobile exchange(MSC1, MSC2), and that the subsystem comprises binary/decimal anddecimal/binary conversion means (31, 41) for converting thesubscriber/equipment identity code, and that the mobile exchange (MSC1,MSC2) comprises means (32, 33, 42) for converting said decimal numberversion into a subscriber/equipment identity code (IMSI, MSIN) complyingwith the numbering scheme of the transmission system, and vice versa. 8.A system according to claim 6, characterized in that said binarysubscriber/equipment identity code is used in the communication betweenthe subsystem and the associated mobile exchange (MSC1, MSC2), and thatthe mobile exchange (MSC1, MSC2) comprises means (31-33, 41, 42) forconverting said binary subscriber/equipment identity code (PID) into thesubscriber/equipment identity code (IMSI, MSIN) complying with thenumbering scheme of the transmission system, and vice versa.
 9. A systemaccording to claim 6, characterized in that the subscriber/equipmentidentity code of the numbering scheme of the transmission system is usedin the communication between the subsystem and the associated mobileexchange (MSC1, MSC2), and that the subsystem comprises means (31-33,41, 42) for converting said binary subscriber/equipment identity code(PID) into the subscriber/equipment identity code (IMSI, MSIN) complyingwith the numbering scheme of the transmission system, and vice versa.